Glass fiber mats have utility as reinforcements for resins, both as laminates and as single layers, carpet backing, wall covering, air and water filtration and high temperature insulation.
In U.S. Pat. No. 3,833,333, assigned to the assignee of the present invention and incorporated herein by reference, a method and apparatus is disclosed for forming continuous strand glass fiber mat. In this patent, a plurality of continuous glass strands are attenuated from a plurality of glass fiber forming positions, with the continuous strands being laid across the width of a mat formation surface by traversing strand attenuators across this mat formation surface and above it and projecting the strands onto the surface from the attenuators.
The orientation of the equipment within this system presents limits to its usefulness. First, the attenuators, which must be traversed above the strand formation surface, comprise a driven belt and a motor for driving this belt. Such an apparatus is quite heavy. When traversing this heavy apparatus across the width of the mat formation surface, its traversing speed is limited due to its high inertia and the impact which must be absorbed at each end of its traverse upon reversing its direction. This speed limitation limits the width of mat which can be efficiently produced at a given density for a specific number of fiber forming and attenuating positions. In addition, for a given width of mat, this limits the rate of production of mat at a given density. It is desirable, therefore, to reduce the weight of the attenuator which must be traversed across the width of the mat formation surface to thereby allow increases in the rate of production of mat and/or the width of the mat which can be efficiently produced.
A second problem incurred when employing the method and apparatus of the prior art system is in the consistency of the strand and mat produced. As is well known in the art, for a given bushing orifice diameter, the diameter of the filaments is inversely proportional to the speed of the attenuation, i.e., increases in attenuation speed produces a smaller diameter filament while decreases in the attenuation speed produces increased filament diameter.
In the above-identified patent, the speed of the belts of the attenuator is maintained constant which projects the strands onto the mat formation surface at a constant rate. However, as the attenuator is traversed away from the filament forming bushings, the total attenuation on the filaments is the sum of the speed of projecting the strands onto the mat formation surface and the speed of traversing the attenuator. But, when the attenuator is traversing the mat formation surface in a direction towards the bushing, the total attenuation on the filaments is the difference between the speed of projecting the strands onto the mat formation surface and the speed of traversing of the attenuator. Thus, for example, having an attenuator projecting strands onto mat formation surface at a constant rate of 2,000 feet/minute (605.80 meters/minute) and traversing across the mat formation surface at a rate of 100 feet/minute (30.48 meters/minute), the filaments are attenuated at varying rates of between 1,900 and 2,100 feet/minute (575.32 and 636.28 meters/minute). This results in inconsistent filament diameters and thus inconsistent density mat being produced.
It is, therefore, a major purpose of the present invention to produce a continuous strand glass fiber mat formation system in which the attenuation rate of the filaments is maintained constant to thereby produce more uniform diameter filaments and a more uniform strand and mat.
It is also a major purpose of the present invention to produce an attenuator or strand advancing apparatus which exerts a constant force on the strands and filaments as it traverses over a mat formation surface.
As used herein, the term "attenuator" refers to an apparatus for attenuating and advancing filaments or an apparatus for advancing previously produced forming packages or bobbins of the strands.